The storage of liquids in tanks characterized by a floating roof structure, is a highly practical way of minimizing liquid vaporization. More specifically, in the instance of storing liquids such as gasoline or the like, use of a roof which is supported by the contained liquid, minimizes the presence of excessive amounts of vapor within the tank, a factor which constitutes a safety hazard due to the volatility of the fumes.
In any liquid holding tank, and in the floating roof type in particular, it is necessary to periodically maintain the integrity of the unit by keeping the sidewalls sufficiently clean. This will assure satisfactory peripheral sealing as the roof moves up and down in response to volumetric changes in the tank's contents. Further, it becomes necessary to periodically clean the tank floor of residue which accumulates over a period of time as solids settle out of the stored liquid.
In any instance, it is usually necessary to empty the tank of stored liquid prior to admitting workmen who will carry out interior cleaning operations.
As the level of the stored liquid drops during an emptying operation, the roof will progressively lower toward the tank floor. Ordinarily, the walls of the tank are clear to permit unimpeded movement of the roof peripheral seal as the roof is adjusted in response to the decreasing level. To avoid interference of the roof with valves, conduits or other hardware in the tank, means is provided to allow the roof to descend to a predetermined level and no lower.
As a matter of practicality, the tank roof is normally provided with adjustable support members which depend downwardly from the roof underside and will contact the tank floor to support the roof when it is at its lowest level. However, when it is desired that the roof be sufficiently high to allow personnel to work in the tank interior, the support members are adjusted by lowering a guided strut and fastening it in place to assure that the desired roof height will be monitored. The lower end of each strut is provided with an enlarged pad or foot that minimizes the amount of compressive stress applied to the tank floor.
The roof-supporting structure, while practical in many respects, does embody several defects. For one thing, due to longitudinal sliding action of the strut within its support sleeve, an annulus will be defined between the two contiguous members. This annulus constitutes a vent opening through which fumes from the tank interior can escape. The unlimited passage of such fumes or gases into the atmosphere can constitute an environmental hazard, which should be avoided.
A further problem which is provoked by escaping gases leaving the tank is the formation of rust or corrosion on parts of the roof support mechanism which are contacted by the fumes as they pass into the atmosphere. It has been found that over a period of time the interior struts can become firmly fixed to the outer guide sleeve, a condition that necessitates a substantial amount of work in breaking the seal to release the interior member.
It can be appreciated that depending on the diameter of the tank, 20 or 30 roof support members may be used, each requiring a considerable investment of time to loosen each stuck member so that the roof can be lowered.
Toward overcoming the stated problem which arise each time a floating roof tank is to be repaired or maintained, there is presently disclosed an improved roof support mechanism that serves two functions. Firstly, it minimizes or precludes the passage of vapors from the contained liquid into the atmosphere. Secondly, it overcomes the problem of the bond formed between the support strut and its guide member due to the corrosive action of the vapors which vent from the tank.
It is, therefore, an objective of the invention to provide a novel and improved liquid storage tank floating roof support.